KIDDE WORRY-FREE AC WIRE-IN SMOKE AND CARBON MONOXIDE ALARM, 5-1/2 IN., 120 VOLTS, 85 DB, 1/EA Sealed-In Lithium Battery Backup-no battery replacement required over the 10 year life of the alarm. Voice message system Peak level memory Smart Interconnect-Interconnects up to 24 Kidde devices Package:1/EA